This invention relates to a chargeable analog electronic timepiece, and in particular, to a charging circuit for a chargeable analog electronic timepiece.
Electronic timepieces having charging circuits are well known in the art and are generally of one of two types. The first type of chargeable electronic timepiece includes a solar battery mounted as part of the dial plate and arranged so that electric power produced by illumination of the solar battery charges the secondary battery.
The second type of chargeable electronic timepiece includes a charging terminal at the external portion of the timepiece arranged so that an electronic power source applied to the timepiece charges the secondary battery when the timepiece is in contact with the external power source. Such a timepiece is well known in the art as exemplified by Japanese Patent Laid-Open Application Nos. 154665/87 and 11846/74 as well Japanese Utility Model Publication No. 4240/81.
Another timepiece of the second type known in the art from Japanese Patent Laid-Open Application No. 29783/86 is an electronic timepiece which includes an electro-magnetic coupling coil disposed within the timepiece and arranged so that the secondary battery is charged when a magnetic field is applied to the electro-magnetic coupling coil from the exterior of the timepiece. Similarly, Japanese Patent Application No. 15035/85 provides an electronic timepiece having a motor coil for driving the timepiece and the coil is separated from the timepiece driving circuit during charging when the magnetic field is applied to the motor coil.
These prior art electronic timepieces have been less than satisfactory. Wrist watches are generally small in size limiting the design of the external appearance, particularly when it is necessary to incorporate a solar battery or charging terminal on the face of the watch. Therefore, it becomes difficult to incorporate a solar battery or charging terminal within an analog electronic wrist watch without damaging the ornamental appearance. Additionally, an electro-magnetic coupling system such as that described in Japanese Patent Laid-Open Application No. 29783/86 requires electronic magnetic coupling coils, rectifying diodes and the like as well as the motor coils for driving the wrist watch resulting in an increased physical size as well as an increase in cost. Furthermore, in the wrist watches utilizing the motor coil to both drive and charge the timepiece, a switch is required to alternately connect the coil for driving the timepiece and for charging the timepiece depending upon the movement of the hand or the charging operation. A rectifying diode is also required within the charging circuit. As a result, design flexibility in a chargeable wrist watch is limited and special regard must be paid to the wrist watch due to the mechanical reliability of the switching mechanism. Additionally, use of the watch is inconvenient because movement of the hands stops during charging requiring resetting of the watch after each charging.
Accordingly, it is desirable to provide a chargeable analog electronic timepiece which overcomes the shortcomings of the prior art devices described above.